1. Field of the Invention
This invention relates in general to high speed printers and, more particularly, to means for moving the print head therein from a starting position across a printing line and returning it to the starting position.
2. Description of the Prior Art
High speed serial printers, both "on-the-fly" and "step-by-step" types, have been meeting with increasing popularity for printing outputs from computers, calculators and other equipment, wherein a print head is moved across a printing line and returned to starting position, and the transport or driving mechanisms for the print heads have proved to be most important. This is true in the many different types of both "impact" and "non-impact" printers. For quality printing, a uniform rate of movement of the print head during printing is essential, but this has been found to be most difficult to attain when extremely high speeds are desired. In this regard, the mass of the print head clearly plays a critical part, even for those printers that are to be used with small devices, such as electronic calculators and instrumentation. This follows from the customary practice of translating the entire print head and its supporting structure across the printing line.
Many types of motion translation means for high speed printer print heads have been developed, some examples of this continuing effort to solve the problems involved being found in the following U.S. Patents.
U.S. Pat. No. 3,300,017 employs a very complex structure (FIGS. 6, 15, 16) for translating print head 334 by a toothed belt 338 in response to energization of electromagnet 615 to unlatch lever 602 so spring 605 will press shoe 601 onto the free end of clutch spring 600 to effect rotation of drive pulley 581. Cam surface 617 resets lever 602 after one revolution of pulley 581, thus releasing the drive of the latter, and a coil spring in the pulley returns the print head to starting position.
U.S. Pat. No. 3,628,645 discloses a drive shaft having two helical grooves in which a pin on the print head rides so that the head is moved from a starting position transversely across the printing line and returned at a higher speed to the starting position in response to rotation of the shaft at a constant speed in only one direction.
U.S. Pat. No. 3,795,298 uses a carriage for the print head which is traversed along a printing line by an endless belt threaded around an idler wheel and a drive wheel, the latter being coupled to a reversible stepping motor.
U.S. Pat. No. 3,572,238 discloses a cable "step-by-step" transverse drive of the printing end of the print head and a transverse following movement of a slide on guide rods, the other end of the print head being pivotally mounted on the slide, with springs interconnecting the slide and the print head, so that the normally undesirable frequency of oscillation is increased to a value the patentee finds more favorable, the printing end being given a step-by-step travel across the printing line and the supporting slide moving transversely with the head as a unit.
U.S. Pat. No. 3,776,340 provides what amounts to step-by-step movements of the printing end of a wire print head relative to the platen, while the print head is moved by a continuous and uninterrupted feed of a head-supporting block parallel to the platen and transversely along a printing line, to prevent relative transverse movement between the printing needles and the platen at the instant of printing impact of the needles. To accomplish this, a shaft through the headsupporting block is provided with an eccentric rotatable in the print head near its printing end, and that shaft is rotated by a motor which also is carried by the headsupporting block, the motor additionally rotating a driving gear meshing with a stationary rack to effect the transverse movement of the block.
In U.S. Pat. No. 3,817,365, but that print head is pivotally supported on a lever which is pivotally mounted on a carriage for moving the print head toward and away from the printing plane and the carriage is moved along guide rails parallel to that plane, the movement of the print head relative to the carriage being employed to withdraw the print head from the printing plane during carriage return following completion of a line of printing and to return it to printing position when the carriage arrives in the beginning of line position.
Thus it will be seen that while pivotal mounting of such a print head has been suggested, it has not been for the purpose of controlling or effecting reciprocable translation of the printing end of the print head to traverse a printing line or area.